Methods for mounting a MEMS sensor for in-stream measurements

ABSTRACT

Systems and methods for packaging a MEMS device to measure the in-stream pressure within a pipe are provided. Embodiments herein avoid the use of a metal housing enclosing the MEMS device or die pad of the MEMS device. Instead, the MEMS device is mounted directly to the pipe using a ceramic carrier. In preferred embodiments, the ceramic carrier is soldered, brazed, welded or eutectic bonded to the metal pipe.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/988,553 filed on Jan. 5, 2016, which is hereby incorporatedby reference in its entirety.

FIELD

The present patent document relates to methods and apparatus forpackaging microelectromechanical systems (MEMS). More particularly, thepresent patent document relates to methods and apparatus for directlymounting a MEMS sensor for in-stream measurements without the use of ametal housing.

BACKGROUND

Typical MEMS packaging systems mount a MEMS device to a die pad and thedie pad is then hermetically sealed to a metal housing. In applicationswhere the sensor is exposed to harsh environments, such as refrigerationand AC systems, a backside entry sensor is used because the top side ofthe sensor, which usually contains the piezo-resistive elements andconnections to the package, cannot be exposed to the harsh conditions inthe environment. The MEMS device is typically mounted on a die pad thatprovides a flange for mounting to the metal housing. The die padincludes a channel or port to the back side of the MEMS device. Theflange of the die pad is then hermetically sealed to the metal housing.The metal housing surrounds the die pad and hermetically seals thechannel or port of the die pad with a channel or port of the metalhousing. The channel or port of the metal housing typically leads to aninterface, such as a threaded interface, that allows the MEMS device tobe coupled to a larger system. To this end, the die pad and metalhousing combine to provide a hermetically sealed channel or port fromthe larger system to the back side of the MEMS device.

Typical MEMS systems including a die pad and metal housing have a numberof deficiencies. For example, a number of different hermetically sealedinterfaces must be executed and executed without defects. The MEMSdevice must be hermetically sealed to the die pad and the die pad mustthen be hermetically sealed to the metal housing. Each one of theseseals must be maintained leak free for the life of the system.

In addition, because the MEMS device, die pad, and housing are usuallymade of different materials, the seals may be subject to thermalmismatch, which can cause cyclical stresses under thermal loading. Overtime, the cyclical stresses due to thermal loading can affect theintegrity of the seals. For all these reasons, the manufacture of MEMSsystems with the typical construction discussed above may be complicatedand include complex processes. These complex processes can lead toincreased costs.

It would be beneficial if MEMS packaging designs could be simplified andsome of the issues addressed above could be eliminated or ameliorated.

SUMMARY OF THE EMBODIMENTS

In view of the foregoing, an object according to one aspect of thepresent patent document is to provide MEMS systems and methods forpackaging MEMS devices. Preferably, the methods and apparatus address,or at least ameliorate one or more of the problems described above. Tothis end, a MEMS system is provided. In one embodiment, the MEMS systemcomprises: a MEMS device including a front side and a backside; aceramic substrate with an opening that traverses the ceramic substratewherein the backside of the MEMS device is hermetically sealed to afirst side of the ceramic substrate around the opening; and, a metalport aligned with the opening and hermetically sealed to the ceramicsubstrate around the opening on an opposite side of the ceramicsubstrate from the MEMS device; wherein the metal port is not formed ina metal housing that surrounds the ceramic substrate.

The MEMS device may be any type of device but is preferably a pressuresensor. If the MEMS device is a pressure sensor, the pressure sensor mayinclude a diaphragm exposed to the opposite side of the ceramicsubstrate through the opening.

In some embodiments, the metal port is a tube. In some of thoseembodiments, the tube is copper.

In some embodiments, the MEMS system further comprises a non-metallichousing that couples to the ceramic substrate on the first side of theceramic substrate and encloses the MEMS device on the first side of theceramic substrate. Preferably, the non-metallic housing is made fromceramic.

In some embodiments, the MEMS system further comprises signalconditioning circuitry for the MEMS device wherein the signalconditioning circuitry is mounted on the first side of the ceramicsubstrate. In some of those embodiments, the non-metallic housing alsoencloses signal conditioning circuitry for the MEMS device mounted onthe first side of the ceramic substrate.

In order to attach the metal port to the ceramic substrate, someembodiments further comprise a metallic layer deposited around theopening on the opposite side of the ceramic substrate between theceramic substrate and the metal port, the metallic layer designed toallow the metal port to be soldered to the substrate.

In another embodiment, a MEMS system is provided that comprises: a MEMSdevice including a front side and a backside; a ceramic substrate withan opening that traverses the ceramic substrate wherein the backside ofthe MEMS device is hermetically sealed to a first side of the ceramicsubstrate around the opening; and, a non-metallic housing that couplesto the ceramic substrate on the first side and encloses the MEMS deviceon the first side of the ceramic substrate.

In such embodiments, the MEMS system may further comprise a metal portaligned with the opening and hermetically sealed to the ceramicsubstrate around the opening on an opposite side of the ceramicsubstrate from the MEMS device. The metal port is not formed in a metalhousing that surrounds the ceramic substrate.

In another aspect of the disclosure provided herein, a method ofpackaging a MEMS device is provided. The method comprises: hermeticallysealing a MEMS device around an opening in a ceramic substrate on afirst side of the ceramic substrate wherein a backside of the MEMSdevice is exposed to an opposite side of the ceramic substrate throughthe opening; mounting signal conditioning electronics for the MEMSdevice on the first side of the ceramic substrate; enclosing the MEMSdevice and signal conditioning electronics on the first side of theceramic substrate with a non-metallic housing; depositing a layer ofmetallic paste around the opening on the opposite side of the ceramicsubstrate; and, hermetically sealing a metal port to the ceramicsubstrate by soldering the metal port to the metallic layer wherein themetal port is not formed as part of a metal housing that surrounds theceramic substrate.

In preferred embodiments, the metal port is a metal tube with an outsidediameter less than an outside diameter of the ceramic substrate. In someembodiments, the metal tube is a copper tube.

In preferred embodiments, the depositing step of the method of packaginga MEMS device is performed by screen printing the metallic paste aroundthe opening.

In another embodiment of a method of packaging a MEMS device, the methodcomprises: hermetically sealing a MEMS sensor around an opening in aceramic substrate on a first side of the ceramic substrate wherein abackside of the MEMS device is exposed to an opposite side of theceramic substrate through the opening; hermetically sealing a metal tubeto the opposite side of the ceramic substrate over the opening whereinthe ceramic substrate has an outside diameter at least twice the outsidediameter of the metal tube

In another aspect of the present patent document, a method of mounting aMEMS sensor to a pipe for in-stream measurement is provided. Suchembodiments are similar to other embodiments disclosed herein except thepipe is the metal port. In one embodiment, the method comprises: forminga first opening through a side of the pipe; forming a flat area on theside of the pipe around the first opening; hermetically sealing a MEMSdevice around a second opening in a ceramic substrate on a first side ofthe ceramic substrate wherein a backside of the MEMS device is exposedto an opposite side of the ceramic substrate through the opening;mounting signal conditioning electronics for the MEMS device on thefirst side of the ceramic substrate; enclosing the MEMS device andsignal conditioning electronics on the first side of the ceramicsubstrate with a non-metallic housing; depositing a layer of metallicpaste around the opening on the opposite side of the ceramic substrate;and, hermetically sealing the ceramic substrate to the flat area in theside of the pipe by soldering the flat area to the layer of metallicpaste.

In preferred embodiments, an area around the pipe may be flattened toall the ceramic substrate to be more easily coupled to the side of thepipe. In yet other embodiments, the pipe may be manufactured with saidflat areas specifically for allowing coupling to sensors.

In some embodiments, the ceramic substrate may be hermetically sealed tothe pipe by soldering the opposite side of ceramic substrate directly tothe pipe over an opening in the pipe using a metallic layer as a metalinterface for the ceramic substrate. The metallic layer may be a layerapplied to the ceramic substrate by screen printing or other depositionmethods prior to soldering.

In yet another aspect of the present patent document, a system formeasuring the in-stream pressure in a pipe is provided. In certainembodiments, the system comprises: a ceramic substrate including a firstside, an opposite side to the first side and a hole that passes throughthe ceramic substrate from the first side to the opposite side whereinthe opposite side of the ceramic substrate is hermetically sealed to aside of the pipe by a solder joint between the ceramic substrate and thepipe; and, a MEMS device hermetically sealed directly to the ceramicsubstrate around the hole on the first side of the ceramic substratewherein a backside of the MEMS device is exposed to the opposite side ofthe ceramic substrate through the hole.

Further aspects, objects, desirable features, and advantages of theapparatus and methods for packaging a MEMS device disclosed herein willbe better understood from the detailed description and drawings thatfollow in which various embodiments are illustrated by way of example.It is to be expressly understood, however, that the drawings are for thepurpose of illustration only and are not intended as a definition of thelimits of the claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exploded view of a MEMS system accordingly to atleast one embodiment of the present patent document;

FIG. 2 illustrates a wireframe view of just the MEMS device coupled tothe substrate;

FIG. 3 illustrates an assembled view of the MEMS system shown in FIG. 1;and,

FIG. 4 illustrates an exploded view of the MEMS system shown in FIG. 1from the opposite side.

FIG. 5 illustrates an exploded view of one embodiment of a MEMS systemfor measuring the in-stream pressure inside a pipe.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates an exploded view of a MEMS system 10 accordingly toat least one embodiment of the present patent document. The embodimentshown in FIG. 1 includes a MEMS device 12, a substrate 14, electronics16, a port 20, and a housing 22. In other embodiments, more or fewercomponents may be present. Embodiments of the present inventioneliminate the metal housing of typical designs. Instead, the MEMS device12 is mated directly to the metal port 20 using a ceramic carrier 14.Preferably, the ceramic carrier 14 is soldered, brazed, welded oreutectic bonded to the metal port 20. Accordingly, the embodimentsdescribed herein reduce the mass of the MEMS system 10, reduce thenumber of hermetic seals in the MEMS system 10, and reduce the costs ofproduction by at least the cost of the metal housing.

In the embodiments described herein, the MEMS device 12 may be any typeof MEMS device. Preferably the MEMS device 12 is a sensor and even morepreferably, the MEMS device is a pressure sensor. In some embodimentswhere the MEMS device is a pressure sensor, the pressure sensor mayinclude a diaphragm.

FIG. 2 illustrates a wireframe view of just the MEMS device 12 coupledto the substrate 14. The MEMS device 12 has a plurality of sides. Forexample, the MEMS device has a front-side 15 and a back-side 17 oppositethe front-side 15. In this particular case, the back-side 17 is definedby the side of the MEMS that couples to the first side 11 of thesubstrate 14. The front-side 15 is the side opposite to the back-side17. In embodiments where the MEMS device 12 is a sensor designed to besubjected to harsh environments, the back-side 17 may be designed to beexposed to such harsh environments through an opening 19 in thesubstrate 14. In some embodiments, the back-side 17 of the MEMS device12 may include a diaphragm that is exposed to the harsh environmentthrough the opening 19. The rest of the MEMS device 12 is isolated fromthe harsh environment by a hermetic seal that surrounds the opening 19between the MEMS device 12 and the substrate 14.

As may be seen in FIG. 2, the substrate 14 may have an opening 19 thattraverses the ceramic substrate 14 from the first side 11 to theopposite side 13 of the substrate 14. The opening 19 may be any size orshape and located anywhere on the substrate 14. Preferably, the opening19 is sized and placed such that the back-side 17 of the MEMS device 12may be hermetically sealed to the first side 11 of the substrate 14around the opening 19.

The substrate 14 may be made from any type of material. In preferredembodiments, the substrate 14 is not metallic. In even more preferredembodiments, the substrate 14 is ceramic.

Returning to FIG. 1, the MEMS system 10 may further include a metal port20. The metal port 20 is aligned with the opening 19 and hermeticallysealed to the opposite side 13 of the substrate 14 around the opening19. In preferred embodiments, the metal port 20 is soldered, brazed,welded or eutectic bonded to the substrate 14. However, in otherembodiments, the metal port 20 may be coupled to the substrate 14 usingother methods. In some embodiments, the metal port 20 may be evencoupled to the substrate 14 with an appropriate adhesive. Once coupledto the substrate, the metal port 20 may provide a metallic interface 27to a channel or port that extends to the back-side 17 of the MEMS device12. To this end, a pressure inlet with a metallic interface 27 isprovided to the MEMS device 12 without the use of a metallic housingthat surrounds or encloses the MEMS device 12.

In preferred embodiments the metal port 20 may be a metal tube. In evenmore preferred embodiments the metal port 20 may be a copper tube.However, in other embodiments, the metal port 20 may be made from anytype of metal including brass, stainless steel, aluminum, titanium orany other type of metal, with or without a threaded end.

Jumping ahead to FIG. 4, in order to couple the metal port 20 to thesubstrate 14 a solderable interface 21 may be provided. In someembodiments, a layer of metallic paste may be deposited on the side ofthe substrate 14 designed to interface with the metal port 20. Thesubstrate 14 may be fired with the layer of metallic paste in order tocreate a solderable interface 21 for the metal port 20. To this end, themetallic paste is preferably deposited around the opening 19. In someembodiments, the metallic paste may be deposited using screen printing.Although the metallic paste may be made from many different substances,it is preferably a type of silver paste. In order to make soldering themetal port 20 to the substrate easier, a solder preform 18 may be used.

As may be seen by returning to FIG. 1, the MEMS system 10 may furtherinclude electronics 16 and a non-metallic housing 22. The electronics 16may include any type of electronics needed by the system. In preferredembodiments, the electronics 16 include signal conditioning electronicsfor the MEMS device 12.

The MEMS system 10 may also include a non-metallic housing 22. In someembodiments, the housing 22 may be made of ceramic. The housing 22preferably couples to the substrate 14 on a first side 11 of thesubstrate 14 and encloses the MEMS device 12 and electronics 16,including the signal conditioning electronics, on the first side 11 ofthe ceramic substrate 12.

As may be seen in FIG. 1, the system 10 does not include a metal housingthat surrounds the MEMS device 12 or the substrate 14 the MEMS device 12is mounted to. Consequently, the metal port 20 is not formed in a metalhousing that surrounds the ceramic substrate. Instead, the metal port 20is mounted directly to the MEMS device 12 via the substrate 14.

Accordingly, in the embodiment shown in FIG. 1, the outside diameter ofthe metal port 20 is significantly smaller than the outside diameter ofthe substrate 14. In some embodiments, the outside diameter of thesubstrate 14 may be twice as big as the outside diameter of the metalport 20. In preferred embodiments, the outside diameter of the substrate14 may be three times, four times, or even five times or more than theoutside diameter of the metal port 20. There is no requirement that theport 20 and/or the substrate 14 be round and where either one is notround, an average distance across may be used to compare the relativesize of the two instead of the outside diameter.

FIG. 3 illustrates an assembled view of the exploded view of the MEMSsystem 10 shown in FIG. 1. As may be seen in FIG. 3, the non-metallichousing 22 may include openings for connecting pins 24 to protrudeoutside the housing 22. This allows electrical communication with theMEMS system within the non-metallic housing 22 even when the system 10is assembled as shown in FIG. 3.

FIG. 5 illustrates an embodiment of the MEMS packaging described hereinmounted directly to the side of a pipe 50. This embodiment is verysimilar to the other embodiments described herein. The main differenceis that the pipe 50 is used in place of the metal port 20. To this end,the pipe 50 may be considered a metal port 20. In order to mount theMEMS device 12 to the pipe 50, the side of the pipe may bepreconditioned. As may be seen in FIG. 5, a portion of the side of thepipe 50 may be flattened to allow the ceramic substrate 14 to be mounteddirectly to the pipe 50. The flattened area includes an opening 52. Theopening 52 goes all the way through the side of the pipe 50. Once theceramic substrate 14 is mounted to the flat area of the pipe 50, theopening 52 provides access between the back side of the MEMS device andthe inside of the pipe 50. This allows the MEMS device 12 to measure thein-stream pressure inside the pipe.

The flattened area 54 may be formed in a number of ways. The pipe may bepress formed, forged, abraded, sanded, or filed down. Side cuts may bemade with a hacksaw or bandsaw. In other embodiments, the pipe may bepreformed with a flat area and hole.

In yet other embodiments, rather than flattening an area of the pipe,the opposite side of the substrate may have a curved surface to fit tothe pipe. To this end, one side of the substrate may be flat formounting to the MEMS device while the other side has a curved surface tomount directly to the curved surface of the pipe.

In preferred embodiments, the substrate 14 is hermetically sealed to theflat area 54 of the pipe 50 by soldering. In order to solder thenon-metallic substrate 14 to the pipe 50, a layer of metallic paste maybe deposited to the opposite side of the substrate 14. The layer of themetallic paste serves as the metal interface on the substrate 14 toallow soldering. In such embodiments, a solder preform 18 may be usedbetween the pipe 50 and the substrate 14.

When creating the opening 52 and flat area 54 in the pipe, they may bemade in any order. As shown in FIG. 5, the flat area 54 is shown as asquare area around a round opening 52. However in other embodiments,other shapes may be used. In preferred embodiments, the flat area 54 isslightly larger than the substrate size. The depth of the flat area 54may vary but needs to be deep enough to provide a flat area 54 formounting around the opening 52.

The methods used herein allow the MEMS device to be mounted directly tothe pipe with only a ceramic substrate in between. This removes thetypical metal housing used in prior methods and reduces costs, thenumber of interfaces, and thermal mismatch issues. The embodimentsdescribed herein may be used to measure any number of aspect about thein-stream flow including but not limited to pressure and temperature. Inaddition, the embodiments have the benefit of being customizable to anypipe diameter after calibration.

Although the embodiments have been described with reference to preferredconfigurations and specific examples, it will readily be appreciated bythose skilled in the art that many modifications and adaptations of theMEMS systems and methods for packaging MEMS devices described herein arepossible without departure from the spirit and scope of the embodimentsas claimed hereinafter. Thus, it is to be clearly understood that thisdescription is made only by way of example and not as a limitation onthe scope of the embodiments as claimed below.

What is claimed is:
 1. A method of mounting a MEMS sensor to a pipe forin-stream measurement comprising: forming a first opening through a sideof the pipe; forming a flat area on the side of the pipe around thefirst opening; hermetically sealing a MEMS device around a secondopening in a ceramic substrate on a first side of the ceramic substratewherein a backside of the MEMS device is exposed to an opposite side ofthe ceramic substrate through the opening; mounting signal-conditioningelectronics for the MEMS device on the first side of the ceramicsubstrate; enclosing the MEMS device and signal-conditioning electronicson the first side of the ceramic substrate with a non-metallic housing;depositing a layer of metallic paste around the opening on the oppositeside of the ceramic substrate; and, hermetically sealing the ceramicsubstrate to the flat area in the side of the pipe by soldering the flatarea to the layer of metallic paste.
 2. The method of claim 1, whereinthe MEMS device is a pressure sensor.
 3. The method of claim 1, whereinthe pressure sensor includes a diaphragm exposed to the opposite side ofthe ceramic substrate through the opening.
 4. The method of claim 1,wherein the flat area is square.
 5. The method of claim 1, wherein thenon-metallic housing is made from ceramic.
 6. The method of claim 1,wherein the layer of metallic paste is screen printed onto the ceramicsubstrate.
 7. The method of claim 1, wherein the ceramic substrate issoldered to the flat area of the pipe with a solder preform.
 8. A methodof mounting a MEMS sensor to a pipe for in-stream measurementcomprising: hermetically sealing a MEMS device around an opening in aceramic substrate on a first side of the ceramic substrate wherein abackside of the MEMS device is exposed to an opposite side of theceramic substrate through the opening; depositing a layer of metallicpaste around the opening on the opposite side of the ceramic substrate;and, hermetically sealing the ceramic substrate to the pipe by solderingthe opposite side of ceramic substrate directly to the pipe over anopening in the pipe using the metallic layer as a metal interface forthe ceramic substrate.
 9. The method of claim 8, wherein the depositingstep is performed by screen printing the metallic paste around theopening.
 10. The method of claim 8, further comprising mounting signalconditioning electronics for the MEMS device on the first side of theceramic substrate.
 11. The method of claim 8, further comprisingenclosing the MEMS device and signal conditioning electronics on thefirst side of the ceramic substrate with a non-metallic housing.
 12. Themethod of claim 11, wherein the non-metallic housing is ceramic.
 13. Themethod of claim 1, wherein the pressure sensor includes a diaphragmexposed to the opposite side of the ceramic substrate through theopening.
 14. A system for measuring the in-stream pressure in a pipecomprising: a ceramic substrate including a first side, an opposite sideto the first side and a hole that passes through the ceramic substratefrom the first side to the opposite side wherein the opposite side ofthe ceramic substrate is hermetically sealed to a side of the pipe by asolder joint between the ceramic substrate and the pipe; and a MEMSdevice hermetically sealed directly to the ceramic substrate around thehole on the first side of the ceramic substrate wherein a backside ofthe MEMS device is exposed to the opposite side of the ceramic substratethrough the hole.
 15. The system of claim 14, further comprising signalconditioning electronics for the MEMS device mounted on the first sideof the ceramic substrate.
 16. The system of claim 15, further comprisinga non-metallic housing that encloses the MEMS device and signalconditioning electronics.
 17. The system of claim 14 wherein the solderjoint couples the side of the pipe to a layer of metallic pastedeposited around the hole on the opposite side of the ceramic substrate.18. The system of claim 14, wherein the ceramic substrate is soldered toa flat area on the side of the pipe.
 19. The system of claim 14, whereinthe MEMS device is a pressure sensor.
 20. The system of claim 19,wherein the pressure sensor includes a diaphragm exposed to the oppositeside of the ceramic substrate through the hole.